Electrografted aryl diazonium initiators for surface-confined photopolymerization: a new approach to designing functional polymer coatings.

This article reports on the preparation of polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-hydroxyethyl methacrylate) (PHEMA) ultrathin grafts on gold substrates modified by 4-benzoylphenyl (BP) moieties derived from the electroreduction of the parent diazonium salt BF(4)(-), (+)N(2)-C(6)H(4)-CO-C(6)H(5) (DS). The grafted organic species -C(6)H(4)-CO-C(6)H(5) was found to be very effective in the surface-initiating photopolymerization (SIPP) of vinylic monomers in the presence of an aromatic tertiary amine co-initiator acting as a hydrogen donor. This novel tandem diazonium salt electroreduction/SIPP was found to be effective in grafting PS, PMMA, and PHEMA from the surface of gold-coated silicon wafers. The polymer films were characterized in terms of chemical structure and wettability by infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy, and contact angle measurements, respectively. The polymer grafts were further evaluated as adsorbents for bovine serum albumin (BSA) used as a model protein. It was found gold/PHEMA resisted BSA adsorption because of its hydrophilic character, whereas PS and PMMA grafts adsorbed BSA via interfacial hydrophobic interaction. The XPS-determined extent of adsorbed BSA was found to increase linearly with the hydrophobic character of the polymer grafts as measured by water contact angles. This work shows that this novel tandem diazonium salt electroreduction/SIPP is a facile, ultrafast, efficient protocol for grafting polymer chains to surfaces. It broadens the enormous possibilities offered by aryl diazonium salts to generate functional organic coatings.